Chronic pain is an undesirable condition that impacts predominantly quality of life at all levels. Chronic pain might occur in healthy young patients when acute postoperative pain is undertreated and persists in time. There are some indexes in the market to evaluate pain, but they assess mainly parasympathetic activity. Hence, it´s a measure of the physiological response to pain, which is still a not well-defined concept. Patients under General Anesthesia might be experimenting unnoticed pain as there is no direct standard method to measure it in clinical practice. This study aims to detect brain oscillatory activity in the intraoperative setting in four situations; awake-no pain, awake-pain, sleep-no pain, and sleep-pain. Pain can be assessed by studying the local and global dynamics of brain activity. A promising upcoming measure of pain could be implemented in clinical practice to detect and treat pain.

This is a pilot study of the presence of neural oscillations during acute pain while awake and in the anesthetized patient with neurophysiological monitoring during a neurosurgery surgical intervention analyzed by electroencephalography.

After the patient's consent, the electroencephalogram is placed in the awake patient and a small painful stimulus is performed based on the channeling of a second venous access. In turn, a recording of the EEG waves is made in order to identify similar neuronal waves during the surgical procedure once the patient is under general anesthesia.

The reason for this intervention is to have a baseline record of each patient without interfering with the oscillations of the different drugs used during total intravenous anesthesia used in these procedures. Normally, after general anesthesia, between 3 and 6 electrodes would be placed on the scalp and 10 electrodes would be placed to carry out this work.

After the intervention, a telephone survey will be carried out on postoperative pain at 3 months and a year.

Inclusion Criteria:

• Adult patients that undergo schedule neurosurgery with neurophysiological monitorisation.
• American Society of Anaesthesiologist physical status (ASA) I-IV.

Exclusion Criteria:

• Pregnancy
• Obstructive hydrocephaly with or with a derivative catheter.
• Patients with neurostimulator
• Emergency surgery.

patients with anaesthesia and eeg monitoring

Research board decision was not to share Individual Participant Data